JPH0643637B2 - Plasma controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plasma control device that performs an etching process or the like in a semiconductor manufacturing process, and more particularly to a plasma control device suitable for forming a fine pattern.

[Conventional technology]

In a technical field of applying discharge plasma to etching, a plasma processing apparatus equipped with a high-frequency power source for accelerating ions in plasma with respect to an electrode on which an object to be etched (for example, a semiconductor wafer substrate) is mounted, There are plasma processing apparatuses described in JP-A-57-131374, JP-A-56-33839, and JP-A-60-160620 for arranging an object to be etched between the electrodes.

In these devices, a high-frequency power source is connected between opposing flat plate electrodes to generate plasma, and a high-frequency power source with a different frequency is connected to the electrode on the substrate mounting side to make the ions incident on the substrate. It controls energy.

The two high-frequency power supplies are both configured to supply power to the plasma, and at this time, a filter circuit is provided so that one of the electrodes can be equivalently regarded as the ground potential for each frequency of the power supply. .

In this conventional configuration, in order to stably supply electric power to the plasma, a matching circuit for each power supply frequency is required not only for the impedance of the plasma but also for the total impedance including the above filter circuit. is there.

As described above, in the conventional plasma processing apparatus, since the filter circuit and the matching circuit include the coil and the capacitor, the frequency band that can be supplied to the plasma is limited, and a waveform other than a sine wave of a specific frequency should be applied. Was difficult.

[Problems to be solved by the invention]

Since the processing accuracy required for etching is about 0.8 μm to 1.3 μm in pattern size, the etching selection ratio between the object to be etched (coating material) and the base material (a predetermined time elapses due to the difference in etching rate). It is necessary to increase (difference in etching between the covering material and the base material) and to perform etching with high dimensional accuracy.

In order to perform such etching, it is necessary to narrow the distribution width of ion energy incident on the object to be etched, to keep the electric field strength between the plasma and the electrode constant, and for this purpose, first, It is an essential technical matter to apply the special waveform including the rectangular wave, the triangular wave, and the higher-order frequency components described in the above publication to the electrodes without blunting the waveform.

It is an object of the present invention to provide a plasma processing apparatus capable of applying a special waveform including high-order frequency components of electrodes without adversely affecting plasma discharge.

[Means for solving problems]

The electrode is grounded through a resistor and a high frequency power source (special waveform generation power source) for supplying power to the resistor is connected, while a high frequency power source for generating plasma, matching circuit, power source side electrode, plasma The problem is solved by an electric system in which the electric circuit consisting of the generation space, the ground side electrode, and the high-pass capacitor is separated.

In other words, a high frequency power supply for generating plasma,
The matching circuit, the electrode on the power supply side, the plasma generation space, the electrode on the ground side, the high-pass filter for passing the frequency of the high-frequency power supply, and the plasma generation electric system composed of a resistor and a capacitor are installed. The solution is to adopt a configuration in which a high frequency power supply for varying the potential of the ground side electrode is superimposed on the resistance.

[Action]

In the above configuration, if the output impedance of the special waveform generating power supply and the impedance of the resistor are matched, the potential of the ground side electrode can be controlled faithfully to the output waveform of the power supply. Sufficient controllability can be provided by using a predetermined resistor having a minimum inductance.

Electric power from the high-frequency power source that contributes to the generation of plasma stably generates plasma by grounding the ground-side electrode through a capacitor that has a sufficiently low impedance at the frequency. Further, it is possible to prevent the electric power from the special waveform generating power source from adversely affecting the plasma. This is for controlling the potential of the ground electrode without passing through plasma.

〔Example〕

Hereinafter, some explanation will be given for convenience in determining the circuit constants of the resistors and capacitors, and then the embodiments will be explained.

In order to control only the potential of the electrode, it is sufficient to generate a potential difference between the electrode and the ground without supplying electric power through plasma.

Conventionally, since the high frequency power is entirely supplied to the plasma, impedance matching is performed between the plasma and the high frequency power supply. Now, let the plasma impedance be a + jb
(A is a resistance component and b is a reactance component),
The imaginary number component jb is usually 1 / jw depending on the capacitive and inductive properties.
The quantity depends on the frequency f (w = 2πf), such as C and jwL. At this time, the power source impedance is a-jb
If so, the reactance component is canceled and the maximum electric power is supplied to the plasma without loss. This is general impedance matching, which is a known principle. (For example, "Glow Disch Processes" by Brian chapman)
arge Processes) (1980) ”On the other hand, since the impedance of plasma, which is a load, changes depending on the type of gas used, pressure, power supplied, etc.
It is difficult to match the impedance of the power source to the fluctuating load each time, and a matching circuit composed of a coil and a capacitor is inserted to match the impedance Z ₀ (output impedance, Z ₀ = r + j0) peculiar to the power source. Therefore, to enable application to a wide frequency component waveform, the combined reactance component of the reactance component of the load impedance and the reactance component of the coil and capacitor in the matching circuit is sufficiently smaller than the resistance component. It is necessary to.

Therefore, as described above, the problem can be solved by configuring the impedance of the load when the electrode to be applied is considered so as not to include the reactance component from the high frequency power supply side. Normally, the output impedance of the power supply is a resistance component of 5
On the other hand, the impedance of plasma is as high as several hundred to several thousand Ω for the resistance component and several thousand Ω for the reactance component, while the impedance of the plasma is about 0 Ω. Therefore, if a resistance smaller than the impedance of the plasma is connected to the electrodes, The potential of the electrodes can be controlled without being affected by the fluctuation of impedance. Moreover, if the resistance value of the resistor is made equal to the output impedance of the power supply, electric power can be supplied without a matching circuit.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

In FIG. 1, 1 is an object to be etched (eg, a semiconductor wafer), 2 and 3 are electrodes facing each other, and 4 is a high frequency.
f _H (eg 13.56MHz) high frequency power supply, 5 is high frequency power supply 4
Matching circuit for, 6 is a low frequency f _L (eg 100KHz)
2 is a high frequency power source, 7 is a resistor having a value equal to the output impedance (for example, 50Ω) of the high frequency power source 6, 8 is a capacitor, and 9 is plasma. The high frequency power supply 6 is composed of a signal generator 6a and a power amplifier 6b. The capacitor 8 has, for example, a capacitance value of 3000 pF, and its impedance is 3.9 Ω for the high frequency f _H 13.56 MHz as shown in FIG. 2, which is smaller than the resistance value of the resistor 7. It is as small as 1/10 (point A in FIG. 2), and is 530Ω for the low frequency f _L 100 KHz, which is more than 10 times the resistance value of the resistor 7 (point B in FIG. 2). .

Next, the operation of this embodiment will be described in detail with reference to FIG. The inside of the apparatus is evacuated by a vacuum pump (not shown), and a reactive gas (for example, carbon tetrachloride,
Freon gas or the like) is introduced and maintained at a predetermined pressure (for example, 1 Pa to several tens Pa) by a pressure control device (not shown).
Since the capacitor 8 connected to the electrode 3 has a low impedance with respect to the frequency f _H of the high frequency power supply 4 as described above, when high frequency power is applied from the high frequency power supply 4 to the electrode 2, the electrode 2 and the electrode 3 are connected to each other. Plasma 9 is generated during this period, and the object to be etched 1 is etched. At this time, the load viewed from the high frequency power source 4 side can be considered as a combined load of the plasma 9 and the capacitor 8, and the combined impedance thereof is exactly the same as the conventional one by adjusting the circuit constant of the matching circuit 5. It can be matched with the output impedance of the high frequency power source 4, and the plasma maintains stable discharge. Regarding the configuration and operation of the matching circuit and impedance matching, JP-A-59-73900 and JP-A-59-130098.
This is a well-known technique as described in Japanese Patent Publication No. 1994-121952, "Glow Discharge Processes" mentioned above, and the like.

Next, when high-frequency power is applied to the electrode 3 from the high-frequency power source 6, the capacitor 8 connected to the electrode 3 has a high impedance with respect to the frequency f _L of the high-frequency power source 6 as described above. Most of the current from the power source 6 flows through the resistor 7, and a potential is generated across the resistor 7. In this case, it is sufficient to consider only the resistor 7 as the load of the high frequency power source 6, and if the resistance value of the resistor 7 is made equal to the output impedance of the high frequency power source 6 (for example, 50Ω), the high frequency
There is no need for a matching circuit for the low frequency f _L corresponding to the matching circuit 5 for f _H. Therefore, for the frequency f _L , by selecting the resistance value of the resistor 7, the impedance matching state can always be established regardless of the frequency of the applied power.

As described above, in the present embodiment, the matching circuit, which is conventionally indispensable between the high frequency power supply 6 and the load (plasma), becomes unnecessary. Further, a filter circuit for preventing the mutual influence of the two high frequency power supplies 4 and 6 is unnecessary. Only the capacitor 8 connected to the electrode 3 is required so that the electrode 3 can be regarded as an earth electrode equivalently for the high frequency power of the frequency f _H. Now, the output from the high frequency power source 6 is, for example, as shown in FIG.
When a rectangular wave having a duty of 50% (T ₁ = 5 μsec) of 100 KHz as in (a) (the rectangular wave includes the highest frequency component), the influence of the 3000 pF capacitor 8 of the present embodiment,
The waveform is as shown in Fig. 3 (b). At this time, the time constant T
₂ has T ₂ = CR = 3000 pF × 50Ω = 0.15 μsec, and the distortion factor (= T ₂ / T ₁ ) of the waveform is only 3%, and there is no problem as an applied waveform for controlling ions. By the way, in the conventional configuration, due to the coil inductance of the matching circuit and the filter circuit, the waveform has a time constant T ₃ = 1.2 μsec and a distortion factor of 24% as shown in Fig. 3 (c), and the rectangular wave is a triangular wave. Could not be applied.

In the above embodiment, the frequency f _{H of the} high frequency power source for generating plasma is 13.56 MHz, the frequency f _{L of the} high frequency power source provided on the substrate mounting side is 100 KHz, the rectangular wave with a duty of 50%, and the capacitor capacity of 3000 pF. Although the output impedance of the power supply is described as 50Ω, the frequency of each power supply is not limited to this, and if the frequency is two high frequency power supplies where f _L and f _H differ by two digits or more, an appropriate capacitor capacity is required. It is needless to say that it is possible to obtain and configure as shown in FIG. 2 in relation to the output impedance of the power source. It is obvious that the present invention is not only effective for a counter electrode type dry etching apparatus, but can also be applied to a μ-wave ECR (Electron Cyclotron Resonance) type dry etching apparatus. This will be described next.

FIG. 4 shows a case where the present invention is applied to a μ-wave ECR type dry etching apparatus. In FIG. 4, the same reference numerals as those in FIG. 1 indicate the same or equivalent portions. In FIG. 4, 20 is a waveguide, 21 is a magnetron, 22 is a coil, and 23 is a processing chamber. A magnetron 21 is attached to one end of the waveguide 20, the other end of the waveguide 20 covers a processing chamber 23, and a coil 22 is provided around the processing chamber 23. Below the processing chamber 23 is an electrode 3 on which an object to be etched 1 (substrate) is placed. The electrode 3 is connected to a high frequency power supply 6 and grounded via a resistor 7 which is a dummy load. The plasma of this device is a μ wave (eg 2.45 GHz) generated by the magnetron 21.
Are generated by electron cyclotron resonance due to the magnetic field of the coil 22. In this case, plasma is generated without electrodes,
It is not necessary to connect the capacitor as in the previous embodiment to the substrate mounting electrode, and it is possible to apply a waveform power having a wide frequency component to the electrode.

As described above, the present invention is not limited to the plasma generation method. Also, plasma processing is not limited to etching, but plasma-based deposition,
Obviously, it can also be applied to polymerization.

As an application of the present invention, for example, the high-frequency power source 6 is composed of a signal generator 6a and a power amplifier 6b, and the signal generator 6a
JP-A-60-12 for making the electric field strength between plasma and electrode constant
A potential waveform for controlling the ions described in 6832 (other than
If the waveform is applied to the electrode on which the substrate is placed, the distribution width of the ion energy incident on the substrate can be narrowed, and the processing dimensional accuracy of etching and the etching target and the base material can be reduced. It is possible to increase the etching rate ratio of several times.

The details will be described with reference to the drawings.

FIGS. 5 (a), (b) and (c) show negative potentials for attracting ions when a waveform 30 for controlling ions is applied from the high frequency power source 6 to the electrode on which the object to be etched 1 is placed. It is the figure which showed the mode of change of the surface potential 33,34,35 of the to-be-etched object 1 when it is set to 40, -80, -120 volts. The horizontal axis represents time and the vertical axis represents potential.

5 (a), (b), and (c) are all the examples shown in FIG. 1, the flow rate of C ₂ clF _{5 is} 30 sccm, the pressure is 8 Pa, and the power of the high frequency power source 4 for generating plasma is 250 W (about 1 W). / Cm ² ). The electrodes 3 on which the substrate is placed are shown in FIGS. 5 (a), (b),
The ion control waveform 30 having a fundamental frequency of 100 KHz shown at the upper side of each of (c) is output from the high frequency power source 6 and applied.

The waveform draws positively charged ions in the plasma by linearly lowering the portion 31 toward the negative side, then raises it to the positive side at the portion 32, and injects electrons with a negative charge to the surface of the wafer. Shaped to neutralize charge.

At this time, the voltage of the portion 31 for attracting ions is set to (a),
When changing to −40V, −80V, −120V as shown in (b) and (c), the surface potential becomes as shown in 33, 34, and 35. State), flat (state where the charge due to the inflowing ions is canceled at the portion 31 of the ion control waveform and the potential is constant), right down (charge due to the inflowing ions is given at the portion 31 of the ion control waveform) The state is smaller than the electric charge). That is,
In the state of (b), the amount of inflowing ions and the amount of supplied electrons due to the control waveform compete with each other, and the charge on the substrate surface becomes constant. Ions are accelerated by an electric field determined by this constant charge. Therefore, the ion energy incident on the substrate becomes constant, and etching with a high processing dimensional accuracy and a high selection ratio with the underlying film becomes possible.

〔The invention's effect〕

As described above, according to the present invention, it is possible to generate a high frequency potential in the electrode without performing a matching circuit when performing plasma processing, and to apply a waveform voltage having a wide frequency component.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an apparatus showing an embodiment of the present invention, FIG.
The figure is for explaining the relationship between frequency and impedance, Figure 3 (a) is a figure showing a rectangular wave shaped to be applied to the electrode, and Figure 3 (b) is for the electrode via a 3000pF capacitor. FIG. 3 (c) is a diagram showing a potential waveform of an electrode when the waveform of (a) is applied through a conventional circuit, and FIG. 4 is another diagram of the present invention. FIG. 5 is a main part configuration diagram of an apparatus showing an embodiment, and FIG. 5 is a diagram showing changes in potential waveforms 33 to 35 when a waveform 30 for controlling ions is applied to electrodes. (c) shows negative potentials of -40, -80, -1 respectively.
It is a figure which shows each relationship when it is 20 volts. 1 ... Etching object, 2, 3 ... Electrode, 4 ... High frequency power supply, 5 ... Matching circuit, 6 ... High frequency power supply, 7 ... Resistor, 8 ... Capacitor, 9 ... Plasma, 20 ... … Waveguide, 21… Magnetron, 22… Coil, 23… Processing room.

Claims (2)

[Claims] 1. A power supply for generating plasma between electrodes arranged in a vacuum chamber, a matching circuit for efficiently propagating output power from the power supply to the plasma, and a matching circuit connected to the matching circuit. An electrode on which a substrate to be processed exposed to plasma is placed, a capacitor connected to the electrode on which the substrate is placed to ground output power from the power source, and a power source for generating the plasma. A second power source that outputs electric power of a frequency lower than a frequency; and a pure resistor that matches the resistance component of the output impedance of the second power source, the second power source and an electrode on which the substrate is placed. A plasma control device having one end connected to and the other end grounded. 2. The plasma control device according to claim 1, wherein the power supply for generating the plasma has a frequency of 13.56 MHz.
Plasma control apparatus, wherein the second power source is a high frequency power source capable of waveform shaping with a fundamental frequency of 100 KHz.